Silver Nanoflower Decorated Graphene Oxide Sponges for Highly Sensitive Variable Stiffness Stress Sensors

Soft conductive materials should enable large deformation while keeping high electrical conductivity and elasticity. The graphene oxide (GO)‐based sponge is a potential candidate to endow large deformation. However, it typically exhibits low conductivity and elasticity. Here, the highly conductive and elastic sponge composed of GO, flower‐shaped silver nanoparticles (AgNFs), and polyimide (GO‐AgNF‐PI sponge) are demonstrated. The average pore size and porosity are 114 µm and 94.7%, respectively. Ag NFs have thin petals (8–20 nm) protruding out of the surface of a spherical bud (300–350 nm) significantly enhancing the specific surface area (2.83 m² g^?1). The electrical conductivity (0.306 S m^?1 at 0% strain) of the GO‐AgNF‐PI sponge is increased by more than an order of magnitude with the addition of Ag NFs. A nearly perfect elasticity is obtained over a wide compressive strain range (0–90%). The strain‐dependent, nonlinear variation of Young's modulus of the sponge provides a unique opportunity as a variable stiffness stress sensor that operates over a wide stress range (0–10 kPa) with a high maximum sensitivity (0.572 kPa^?1). It allows grasping of a soft rose and a hard bottle, with the minimal object deformation, when attached on the finger of a robot gripper.     

Thermal and electrical conductivity of Al(OH)<Subscript>3</Subscript> covered graphene oxide nanosheet/epoxy composites

Al(OH)₃ functionalized graphene composites (Al–GO) were prepared using a simple sol–gel method. In this protocol, graphene oxide (GO) was prepared according to the Hummers method and functionalized to enhance its reactivity with aluminum isopropoxide by a LiAlH₄ treatment. The functionalized graphene sheets were characterized by X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy. These analyses confirmed that GO had been fabricated and the Al(OH)₃ layer could have a homogeneous distribution with large and dense coverage onto GO sheets. In addition, the thermal and electrical conductivity of the epoxy composites with GO and Al–GO fillers were measured. The thermal conductivities of the composites with graphene-based fillers were enhanced by the addition of fillers. In particular, the thermal conductivity of GO/epoxy composite containing 3 wt% was approximately two times higher than that of pure epoxy resin. In addition, the electrical conductivity of Al–GO embedded composites degenerated compared to GO composites.     

Coupled electro-mechanical properties of multiwall carbon nanotube/polypropylene composites for strain sensing applications

The electrical, mechanical, and coupled electro-mechanical (piezoresistive) properties of multiwall carbon nanotube/polypropylene (MWCNT/PP) composites at four MWCNT concentrations above electrical percolation (4–10 wt %) were investigated. The electrical conductivity of the composite increased monotonically from 0.77 to 15.0 S/m with the increase of MWCNT concentration. The elastic modulus also increased monotonically with increased MWCNT concentration with the concomitant reduction of ultimate strain. The coupled signal between electrical resistance and applied strain during tensile loading displayed a marked change toward higher sensitivity at the elastic-to-plastic transition zone of the polymer composite, which allowed the identification of polymer yielding by the sole monitoring of electrical resistance. Large ratios (of the order of 15–29) of normalized changes in electrical resistance over applied strain (“gage factor”) were found in the plastic zone, and such electro-mechanical sensitivity was higher for composites with lower MWCNT content.     

Effect of processing technique on the transport and mechanical properties of graphite nanoplatelet/rubbery epoxy composites for thermal interface applications

Graphite nanoplatelet (GNP)/rubbery epoxy composites were fabricated by mechanical mixer (MM) and dual asymmetric centrifuge speed mixer (SM). The properties of the GNP/rubbery epoxy were compared with GNP/glassy epoxy composites. The thermal conductivity of GNP/rubbery epoxy composite (25 wt.% GNP, particle size 15 μm) reached 2.35 W m⁻¹ K⁻¹ compared to 0.1795 W m⁻¹ K⁻¹ for rubbery epoxy. Compared with GNP/rubbery epoxy composite, at 20 wt.%, GNP/glassy epoxy composite has a slightly lower thermal conductivity but an electrical conductivity that is 3 orders of magnitude higher. The viscosity of rubbery epoxy is 4 times lower than that of glassy epoxy and thus allows higher loading. The thermal and electrical conductivities of composites produced by MM are slightly higher than those produced by SM due to greater shearing of GNPs in MM, which results in better dispersed GNPs. Compression and hardness testing showed that GNPs increase the compressive strength of rubbery epoxy ∼2 times without significantly affecting the compressive strain and hardness. The GNP/glassy epoxy composites are 40 times stiffer than the GNP/rubbery epoxy composites. GNP/rubbery epoxy composites with their high thermal conductivity, low electrical conductivity, low viscosity before curing and high conformability are promising thermal interface materials.     

Chemical and thermal reduction of graphene oxide and its electrically conductive polylactic acid nanocomposites

Graphene oxide (GO) was reduced with biocompatible glucose and polyvinylpyrrolidone (PVP) and incorporated in polylactic acid (PLA). The thermal reduction of GO during the compression molding of PLA was also studied to delineate the reduction efficiencies from thermal and chemical processes. Results indicate that glucose is more effective in the reduction of GO (rGO-g) with a much higher electrical conductivity than PVP and thermally treated GO. Even rGO-g was also highly efficient in improving the electrical conductivity of PLA. The composite with ∼1.25 vol.% of rGO-g exhibited a high conductivity of ∼2.2 S/m due to the chemical reduction of GO with glucose and the thermal reduction of rGO-g during the compression molding process.     

Effect of interfacial features on the mechanical and electrical properties of rGO/Al composites

This study investigates the effect of interfacial features on the mechanical and electrical properties of reduced graphene oxide (rGO)/aluminum (Al) composites. The composites were fabricated using a hybrid process that includes chemical and mechanical methods. First, GO was uniformly dispersed on the surface of Al powder via a solution process. A strong interface was formed between GO and Al via several chemical bonds by using polyvinyl alcohol (PVA) as an organic binder during the solution process. Then, GO was thermally reduced to rGO, wherein the interfacial features were varied according to the atmosphere (vacuum or H₂(10%)/N₂(90%) mixed gas). Subsequently, rGO was mechanically embedded and further dispersed within soft Al powder through the plastic deformation of Al. Vacuum was found to be more effective than the mixed gas at removing functional groups containing oxygen in GO and therefore generated a tighter interface. As a result, the composites containing rGO that were reduced under vacuum showed higher strength and lower ductility compared with those reduced under the mixed gas. Conversely, the interfacial features rarely affected the electrical conductivity of the composites because the electrical conductivity of rGO was considerably lower than that of Al. Consequently, compared with their monolithic counterparts, the composites containing only 0.2 vol% rGO showed a 374-MPa yield strength without a significant loss of electrical conductivity, thereby demonstrating their potential feasibility in electrical and electronic applications.     

Preparation of highly conductive graphene-coated glass fibers by sol-gel and dip-coating method

In order to fabricate highly-conductive glass fibers using graphene as multi-functional coatings, we reported the preparation of graphene-coated glass fibers with high electrical conductivity through sol-gel and dip-coating technique in a simple way. Graphene oxide (GO) was partially reduced to graphene hydrosol, and then glass fibers were dipped and coated with the reduced GO (rGO). After repeated sol-gel and dip-coating treatment, the glass fibers were fully covered with rGO coatings, and consequently exhibited increased hydrophobicity and high electrical conductivity. The graphene-coated fibers exhibited good electrical conductivity of 24.9 S/cm, being higher than that of other nanocarbon-coated fibers and commercial carbon fibers, which is mainly attributed to the high intrinsic electrical conductivity of rGO and full coverage of fiber surfaces. The wettability and electrical conductivity of the coated fibers strongly depended on the dip-coating times and coating thickness, which is closely associated with coverage degree and compact structure of the graphene coatings. By virtue of high conductivity and easy operation, the graphene-coated glass fibers have great potential to be used as flexible conductive wires, highly-sensitive sensors, and multi-functional fibers in many fields.     

Graphene/thermoplastic polyurethane nanocomposites: Surface modification of graphene through oxidation,polyvinyl pyrrolidone coating and reduction

Herein, oxidation, polyvinyl pyrrolidone (PVP) coating and reduction are used to modify the surface of graphene in thermoplastic polyurethane (TPU)/graphene nanocomposites. It is demonstrated that graphene could be easily dispersed in TPU with PVP absorbed on reduced graphene oxide (RGO) as stabilizer during reduction. In the stress–strain curves for these composites containing GO, PVP coated GO (GO/PVP) and reduced GO/PVP (RGO/PVP) as filler, PVP coating and reduction can largely enhance the stress in low modulus region. It is thought to largely related with enhanced interfacial interaction between filler and matrix and healing of graphene structure during reduction. Consequently, the modulus of TPU/GO/PVP and TPU/RGO/PVP is significantly increased. Meanwhile, an electrical percolation threshold of 0.35 wt.% is obtained for TPU/RGO/PVP. Comparing with the results in literature, the filler surface modification used in this study has created nanocomposites with a good balance between electrical conductivity and mechanical properties.     

苯胺共聚物含量对氧化石墨嵌入复合物结构与性能的影响

以氧化石墨(GO)为主体, 苯胺-邻甲氧基苯胺导电共聚物(P(An-co-oAs))为客体, 采用剥离/重新组装技术合成出P(An-co-oAs)嵌入GO复合材料. FTIR分析显示, P(An-co-oAs)的N-H基团与GO片层中的C=O基团存在着氢键作用. XRD和TEM分析表明, P(An-co-oAs)/GO保持良好的层状结构, 且随着P(An-co-oAs)含量的增加, 复合材料的层间距不断扩大. P(An-co-oAs)的插入, 使得复合材料的室温电导率比GO提高2～3个数量级. 同时发现, 增加P(An-co-oAs)的含量, 不仅提高了GO的电化学活性, 也改善了GO的锂离子嵌入/脱嵌的循环稳定性.     

聚苯胺/石墨导电复合材料的制备与表征

根据石墨的层状结构，以可膨胀石墨（KP）或膨胀石墨（EP）为模板，应用原位聚合法成功制备了聚苯胺（PANi)石墨导电复合材料。通过FT－IR、XRD、SEM和电导率测量等手段表征了其结构和性能。结果表明，PANi/EP的电导率与单一组分相比，都有大幅度提高，而PANi／KP的电导率介于两组分之间，PANi/EP的电导率高于PANi/KP复合材料4－5倍。XRD证明，膨胀石墨与聚苯胺复合大大提高了聚苯胺的结晶度，改善了聚苯胺的结构缺陷。FT－IR表明聚苯胺的特征吸收峰发生了位移，表明KP或EP的表面官能团与聚苯胺之间发生了氢键或共轭作用。     

热处理条件对氧化石墨结构和导电性能的影响

氧化石墨是石墨的氧化产物．由于它的碳层表面引入了很多极性功能团，使得很多分子都能够嵌入其层间形成纳米复合物，但也正是这些功能团使得它散失了石墨良好的导电性。为了考察氧化石墨受热处理后还原的可能性，通过X-射线衍射、扫描电镜、红外光谱分析以及元素分析等手段研究了氧化石墨在不同热处理条件下的结构变化。研究发现热处理时的升温速度对氧化石墨的结构影响很大，快速升温时，氧化石墨迅速分解，发生膨胀形成类似于膨胀石墨的含有丰富的50nm至5μm左右孔洞的一种结构；而当缓慢升温时，氧化石墨随着热处理温度的升高，逐渐恢复成类似于石墨的结构，同时电导率也随热处理温度的升高而提高，当热处理温度高于180℃时，电导率大于1S／cm。这些结果表明利用氧化石墨作为前驱体，通过先制备聚合物／氧化石墨纳米复合物后经热处理来得到导电性的聚合物／碳纳米复合材料是可行的。     

Highly conductive graphene oxide/polyaniline hybrid polymer nanocomposites with simultaneously improved mechanical properties

Graphene oxide (GO) was added to a polymer composites system consisting of surfactant-wrapped/doped polyaniline (PANI) and divinylbenzene (DVB). The nanocomposites were fabricated by a simple blending, ultrasonic dispersion and curing process. The new composites show higher conductivity (0.02–9.8 S/cm) than the other reported polymer system filled with PANI (10⁻⁹–10⁻¹ S/cm). With only 0.45 wt% loading of GO, at least 29% enhancement in electric conductivity and 29.8% increase in bending modulus of the composites were gained. Besides, thermal stability of the composites was also improved. UV–Vis spectroscopy, X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM) revealed that addition of GO improves the dispersion of PANI in the polymer composite, which is the key to realize high conductivity.     

MWCNT/PEDOT复合材料的微观结构和热电性能

热电转换技术能将大量的废弃热能转换为电能以重新利用,是一种绿色能源转换技术,可以有效提高能源利用效率,缓解煤炭、石油等主要化石类能源过度开采、使用带来的能源危机及环境污染问题,因此受到科研工作者的广泛关注,是近年来的研究热点。基于此,本文以电子型导电高聚物中机能较优的聚(3, 4-乙烯二氧噻吩)(PEDOT)作为研究主体,通过化学原位氧化聚合将多壁碳纳米管(MWCNT)复合到载体中得到MWCNT/PEDOT复合材料。利用XRD、拉曼、TEM及正电子湮没寿命(PAL)等方法对MWCNT/PEDOT复合材料的形貌和微观结构进行了系统研究,研究表明:当MWCNT含量高于24.9wt%时,复合材料中出现MWCNT团聚现象,其分散性变差。同时,MWCNT/PEDOT复合材料的热电性能测试结果显示,未掺杂PEDOT的电导率仅为7.5 S·m?1,而MWCNT含量为30.1wt%时,该复合材料的电导率高达566.59 S·m?1,提高近76倍。同时,30.1wt%MWCNT/PEDOT的功率因子(814.3×10?4 μW·(m·K2)?1)相对于未掺杂PEDOT(14.5×10?4 μW·(m·K2)?1)提高约56倍,这主要是由于PEDOT分子链与MWCNT掺杂物间π-π相互作用及MWCNT的高导电性。随着MWCNT含量的增加,PAL测试结果中第一寿命成分τ₁(即正电子在材料中湮没的第一寿命成分)的下降证实了该复合材料中MWCNT与PEDOT间界面变小或者界面间相互作用减弱,导致其热导率相对于未掺杂PEDOT有一定的上升,但远远低于功率因子的升高。最终,该MWCNT/PEDOT复合材料的热电优值(即热电材料Z_T值)由0.015×10?4升至0.45×10?4,增加了约30倍。结果表明:掺杂的高电导率MWCNT能够极大地提高PEDOT类电子型导电聚合物的热电性能。      

Processing and bioactivity of 45S5 Bioglass®-graphene nanoplatelets composites

Well dispersed 45S5 Bioglass^® (BG)-graphene nanoplatelets (GNP) composites were prepared after optimising the processing conditions. Fully dense BG nanocomposites with GNP loading of 1, 3 and 5 vol% were consolidated using Spark plasma sintering (SPS). SPS avoided any structural damage of GNP as confirmed using Raman spectroscopy. GNP increased the viscosity of BG-GNP composites resulting in an increase in the sintering temperature by ~50 °C compared to pure BG. Electrical conductivity of BG-GNP composites increased with increasing concentration of GNP. The highest conductivity of 13 S/m was observed for BG-GNP (5 vol%) composite which is ~9 orders of magnitude higher compared to pure BG. For both BG and BG-GNP composites, in vitro bioactivity testing was done using simulated body fluid for 1 and 3 days. XRD confirmed the formation of hydroxyapatite for BG and BG-GNP composites with cauliflower structures forming on top of the nano-composites surface. GNP increased the electrical conductivity of BG-GNP composites without affecting the bioactivity thus opening the possibility to fabricate bioactive and electrically conductive scaffolds for bone tissue engineering.     

Enhancement of electroconductivity of polyaniline/graphene oxide nanocomposites through in situ emulsion polymerization

The present study introduces a systematic approach to disperse graphene oxide (GO) during emulsion polymerization (EP) of Polyaniline (PANI) to form nanocomposites with improved electrical conductivities. PANI/GO samples were fabricated by loading different weight percents (wt%) of GO through modified in situ EP of the aniline monomer. The polymerization process was carried out in the presence of a functionalized protonic acid such as dodecyl benzene sulfonic acid, which acts both as an emulsifier and protonating agent. The microstructure of the PANI/GO nanocomposites was studied by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, UV–Vis spectrometry, Fourier transform infrared, differential thermal, and thermogravimetric analyses. The formed nanocomposites exhibited superior morphology and thermal stability. Meanwhile, the electrical conductivities of the nanocomposite pellets pressed at different applied pressures were determined using the four-probe analyzer. It was observed that the addition of GO was an essential component to improving the thermal stability and electrical conductivities of the PANI/GO nanocomposites. The electrical conductivities of the nanocomposites were considerably enhanced as compared to those of the individual PANI samples pressed at the same pressures. An enhanced conductivity of 474 S/m was observed at 5 wt% GO loading and an applied pressure of 6 t. Therefore, PANI/GO composites with desirable properties for various semiconductor applications can be obtained by in situ addition of GO during the polymerization process.     

原位氨基化氧化石墨烯/聚酰亚胺复合材料的制备及性能

以1,4-双（4-氨基-2-三氟甲基苯氧基）苯（6FAPB）和3,3',4,4'-二苯醚四酸二酐（ODPA）为合成聚酰亚胺（PI）的单体,首先采用原位氨基化方法使氧化石墨烯（GO）与6FAPB反应转变为原位氨基化GO,再与ODPA和剩余的6FAPB发生聚合反应得到原位氨基化GO/聚酰胺酸（PAA）溶液。涂膜后,经热酰亚胺化制备出GO质量分数分别为0.05wt%、0.1wt%、0.3wt%、0.5wt%和1.0wt%的原位氨基化GO/PI复合材料膜。利用FTIR、XPS、XRD、UV-vis、TGA、TMA、SEM、拉伸性能测试及接触角测试对原位氨基化GO/PI复合材料的结构和性能进行表征。结果表明,原位氨基化使GO以化学键与PI大分子链连接,有利于GO在复合材料基体中的稳定和均匀分散。XRD结果表明,所得到的原位氨基化GO/PI复合材料膜均为无定型结构。随GO质量分数增加,原位氨基化GO/PI复合材料薄膜的光学透明性急剧降低,但力学性能和热稳定性有一定提高。当GO的质量分数为1.0wt%时,原位氨基化GO/PI复合材料的拉伸强度由64 MPa增加到83 MPa,杨氏模量由1.67 GPa提高到2.10 GPa,10%热失重温度由593℃增加到597℃,玻璃化转变温度变化不大。由于热酰亚胺化后GO表面的大部分含氧官能团消失,原位氨基化GO/PI复合材料膜的吸水率由0.86%降低至0.58%,水接触角由72.5°增加到77.8°。     

Design and preparation of graphene/poly(ether ether ketone) composites with excellent electrical conductivity

Graphene/poly(ether ether ketone) (m-TRG/PEEK) composites with excellent electrical conductivity were fabricated by hot pressing technique with thermally reduced graphene nanosheets (m-TRG) which were modified by poly(ether sulfone). Moreover, the conductive, thermal, and mechanical properties of PEEK/m-TRG composites were investigated by the precision impedance analyzer, thermal gravimetric analyzer, differential scanning calorimetry, and universal tester, respectively. The electrical conductivity of m-TRG/PEEK composites was greatly improved by incorporating graphene, resulting in a sharp transition from electrical insulator to semiconductor with a low percolation threshold of 0.76 vol.%. A high electrical conductivity of 0.18 S m^?1 was achieved with 3.84 vol.% of m-TRG. The data were compared with those of composites reduced chemically, and the results showed that thermal reduction was an effective method to acquire higher electrical conductive composites. The excellent electrical property should be attributed to the large specific surface area of m-TRG, well dispersion of m-TRG in PEEK matrix, and good compatibility of m-TRG with PEEK matrix, as proven by scanning electron microscope. Besides, m-TRG/PEEK composites also exhibited relatively good thermal and mechanical properties.     

L-半胱氨酸还原氧化石墨烯的研究

采用改进Hummers法合成氧化石墨,在水中超声分散获得氧化石墨烯水溶胶,并加入L-半胱氨酸于95℃进行回流反应后得到还原氧化石墨烯。采用X射线衍射仪、傅里叶变换红外光谱仪和热重-差热扫描仪等探讨氧化石墨烯还原前后的结构与性能变化。结果表明,L-半胱氨酸能有效还原氧化石墨烯,且还原后的氧化石墨烯在乙醇中有较好的分散性,其所制薄膜的导电率为500S/m。由此法制备的石墨烯有望广泛应用于电子、光电、电容器和传感器等器件中。     

反应条件对石墨烯/银导电性能的影响研究

通过改进石墨烯/银制备过程中的制备温度、pH值以及不同还原剂的选择,研究了反应条件对石墨烯/银复合材料导电性能的影响。结果表明:在氧化石墨烯制备过程中,实验温度对石墨的剥落起到了关键作用,相对于一步法,多步法制备的氧化石墨烯层数更低、纯度更高、导电性能更好;复合过程中pH值的调节能够改变银在氧化石墨烯表面的沉降率,当pH值为12时,银的沉降密度最大,产物的电导率更高,达5.3×10~2 S/m;在进行氧化石墨烯材料的还原时,同等条件下,NaBH_4的还原效果要优于柠檬酸三钠和Vc的还原效果,经NaBH_4还原的r GO和rGO/Ag的电导率分别为0.46×10~4,7.32×10~4 S/m,且经NaBH_4还原的rGO/Ag制备的导电油墨,具有与商业导电银浆相媲美的电阻值。     

Fast and facile graphene oxide grafting on hydrophobic polyamide fabric via electrophoretic deposition route

Fabric surface coating is deemed as the major route to fabricate functional fabrics, and interface stability is a critical factor affecting the performance of fabric. Here, electrophoretic deposition (EPD) is employed for fast and facile modification of hydrophobic polyamide fabric with graphene oxide (GO) nanosheets embedded in polymeric networks. For better grafting, polyethyleneimine is utilized to modify the surface of the fabric substrate, endowing more polar groups and resulting in reasonable interface properties of graphene oxide and fabric substrate. GO nanosheets are uniformly deposited on modified fabric via EPD method and then reduced by green hot-press processing. The modified fabric shows excellent electrical conductivity (electrical conductivity?>?3.3 S/m), thermal conductivity (0.521 W/m·K), and UV protection performance (UPF?>?500, UVA?<?0.2%). Meanwhile, the contact angle test of fabric reveals that the addition of graphene significantly improved the hydrophobicity of the fabric.